Best test to diagnose gastroesophageal reflux disease and quantity acid output is

.for GERD, THE INVESTIGATIONS can be, *24 hours oesophageal pH monitoring is regarded as the gold standard.PPI should be stopped for 3 weeks prior to pH monitoring. *barium study in head down position. *endoscopy to exclude other diseases. *oesophagal manometry to assess the state of lower oesophagal sphincter. Ref: SRB&;s manual of surgery,5th ed, pg no 792